Method of treatment of wood pulp for greater efficiency in wood utilization

ABSTRACT

The addition of certain surfactant polyoxyethylene polyoxypropylene block copolymers in the sulfate pulping process results in increased yields of pulp.

United States Patent Parker et a1.

[451 Sept. 30, 1975 METHOD OF TREATMENT OF WOOD PULP FOR GREATEREFFICIENCY IN WOOD UTILIZATION Inventors: Edward T. Parker, lnkster;Lester G. Lundsted, Grosse 11e, both of Mich.

BASF Wyandotte Corporation, Wyandotte, Mich.

Filed: Dec. 14, 1972 Appl. No.: 314,957

Assignee:

References Cited UNITED STATES PATENTS 9/1961 Mitchell et a1 162/72Jackson et a1 260/615 B Jackson et a1 260/615 B OTHER PUBLICATIONS CaseyPulp and Paper Second Ed., Vol. 11, pp. 223-227.

Primary E.\'aminerS Leon Bashore Assistant ExaminerPeter Chin Attorney,Agent, or Firm-Norbert M. Lisicki; Bernhard R. Swick; Robert E. Dunn [57 1 ABSTRACT The addition of certain surfactant polyoxyethylenepolyoxypropylene block copolymers in the sulfate pulping process resultsin increased yields of pulp.

5 Claims, No Drawings BACKGROUND OF THE INVENTION 1. Field Of TheInvention The present invention relates to preparation of pulpwood usingthe sulfate pulping process. More specifically, the present inventionrelates to improvements in yield of pulp per ton of wood digested by theuse of certain polyoxyethylene polyoxypropylene digester additives.

2. Prior Art The cellulosic and non-cellulosic carbohydrate fiberspresent in wood are held together to form a semiplastic solid by lignin,a complex polymer composed of hydroxyphenylpropane units. This complexpolymer binds the wood fiber partially by an amalgamation between thefiber walls, by an absorption within the fiber walls and partially, itis believed, by chemical bonding between the cellulose and the lignin.Delignified, or partially delignified, cellulose fibers are required forthe production of certain papers and pulp products. In the sulfateprocess for the preparation of pulpwood, a solution of sodium hydroxideand sodium sulfide :is used to degrade the lignins to obtain thesecellulose fibers. To degrade these materials,'moderately hightemperatures and pressures are employed to expedite the penetration anddiffusion of the sodium, sulfide and hydroxyl ions into the woodstructure. As far as we know, the use of additives to increase thispenetration resulting in increased yields has not been successful; Atthe present rate of production, wood supplies are being rapidly depletedin spite of industry efforts to encourage reforestation on privatelands, and to practice tree planting and controlled cutting on its ownlands. Other forms of wood salvage such as the use of barked and Ichipped sawmill waste, slabs, edgings and plywood cores have beenfollowed up to obtain raw materials. Even the utilization of sawmillsawdust has been employed. It is quite evident that any improvements inyield would be welcomed by the pulp and paper industry.

One of the major advantages of the sulfate pulping process is itsability to pulp both coniferous and deciduous wood in greater varietythan other processes. Among the coniferous species which can be pulpedare the Western-red cedar, Cypress, Balsam fir, Noble fir, White fir,Douglas fir, Canadian and Western Hemlock, Larch, Loblolly pine,Ponderosa pine, White pine and Redwood, and of the spruce species,Engelman, Sitka, and White. The deciduous species which can be used are:Ash, Basswood, Beech, Birch, Chestnut, Elm, Gum, Red and Sugar Maple,Northern, Post and White Oak, Sweetgum, the Big Leaf and QuakingPoplars, and the Tulip trees.

SUMMARY OF THE INVENTION It has now been discovered that the addition ofminimal amounts of certain surfactant polyoxyethylene polyoxypropylenedigester additives to the sulfate liquor results in an increased yieldof pulp per ton of wood used, with no corresponding loss of pulpbrightness, tensile and bursting strength.

DESCRIPTION OF THE PREFERRED EMBODIMENT The wood chips which are to bepulped are charged to the pulping basket on an oven-dry wood basis. Themoisture content of the wood must be determined as it is desirable tomaintain the liquor-to-wood ratio within certain ranges. Theliquor-to-wood ratio can vary from about 2/1 to about 6/1, preferablyfrom about 3/1 to about 5/1. The moisture content of the wood cancontribute as much as 50 percent of the water present in the cookingliquor. Knowing the moisture content of the wood chips, the cookingliquor is prepared by dissolving the required amounts of sodiumhydroxide (NaOH) and sodium sulfide (Na S) in water. The percentage oftotal active alkali to be used depends on the species of wood to bepulped and on the degree of delignification of the wood desired, i.e.,whether a board grade of pulp with moderate delignification or ableaching grade of pulp with as much delignification as possible isbeing made. This concentration generally varies from about 12 percent toabout 25 percent total active alkali, preferably from about 15 percentto about 22 percent. Total active alkali is expressed as percent sodiumoxide (Na O) based on the oven dry weight of the wood charged to thedigester. This Na O represents both the amount of NaOH and Na S to beused. The Na S used will furnish about 15 percent to about 25 percent ofthe total Na O, while the remainder will be furnished by the NaOH. Inactual plant practice, some of the pulping liquor may be recirculated sothat the total Na O content may include salts such as sodium carbonate,sodium hydrosulfide, sodium sulfate and sodium thiosulfate. This is dueto the addition of some black liquor to freshly prepared cooking liquor.The black liquor is that liquor which is obtained from a previouspulping run and may constitute from about 10 percent to about 50 percentof the cooking liquor added to a fresh charge of wood chips.

Also of interest is the sulfide content of the cooking liquor. This isusually expressed as Sulphidity which is the percentage ratio of Na S,expressed as Na O, to the total active alkali.

The digester additive is best added to the cooking li- 'quor before itis circulated through the wood chips.

After the sulfate cooking liquor has circulated through the wood chipsfor about five minutes, the air in the digester is purged and steam isallowed to enter the digester to its maximum pressure which may rangefrom to psig. The temperature may range from about 250 F. to about 400F., preferably from about 300 F. to about 375 F. This temperature andpressure are maintained from about 0.5 hour to about 6 hours,preferably, from about 0.5 hour to about 3 hours.

At the end of the required time at the specific temperature andpressure, the digester is blown to the blow tank, the weak black liquordrained, and the pulp is then coarse screened and washed by suchprocesses as are well known to those skilled in the art.

The surfactant additives contemplated for use in the subject inventionare essentially those disclosed by D. R. Jackson et al. in US. Pat. No.3,036,l l8 issued on May 22, 1962. These are surface active agentsobtained by condensing ethylene oxide with a low molecular weightreactive hydrogen compound forming a polyoxyethylene polyol and thenfurther condensing this polyol with propylene oxide. The structuralformula of these surfactants corresponds to Ru mi m smmmw wherein R isthe nucleus of a reactive hydrogen compound, x has a value of 2 to 6, mhas a value such that the oxypropylene chain has a molecular weight fromabout 900 to 25,000, preferably from 900 to 5,000, and n has a valuesuch that the weight of oxyethylene groups constitutes from about to 90weight percent, preferably 10 to 60 weight percent, of the mixture. Theconcentration of surfactant may vary from about 0.05 percent to 1.0percent, preferably from about 0.1 percent to 0.5 percent, based on theweight of oven dry wood.

The above surfactants are prepared by the reaction of propylene oxidewith an ethylene oxide condensate of a reactive hydrogen compound. Thereactive hydrogen compound must be a relatively low molecular weight,water-soluble compound having at least two and preferably not more thansix reactive hydrogen atoms. One class of such compounds is the lowmolecular weight, aliphatic, polyhydric alcohols such as ethyleneglycol, propylene glycol, 2,3-butylene glycol, 1,3- butylene glycol,1,5-pentanediol, 1,6-hexanediol, glycerol, trimethylolpropane, sorbitol,sucrose and the like. Other classes that can be used are alkylamines,alkylene polyamines, cyclic amines, amides and polycarboxylic acids.These surfactants and their method of preparation are adequatelydescribed in the aforementioned patent, U.S. Pat. No. 3,036,118.

The surfactants employed in the following examples are defined asfollows:

Nonionic No. 1 is a polyoxypropylene adduct of a polyoxyethylene glycolwherein the polyoxypropylene chain has a molecular weight of about 1700and the oxyethylene content is about percent by weight of the mixture.

Nonionic No. 2 is a polyoxypropylene adduct of a polyoxyethylene glycolwherein the polyoxypropylene chain has a molecular weight of about 2200and the oxyethylene content is about percent by weight of the mixture.

Nonionic No. 3 is a polyoxypropylene adduct of a polyoxyethylene glycolwherein the polyoxypropylene chain has a molecular weight of about 2500and the oxyethylene content is about 25 percent by weight of themixture.

Nonionic No. 4 is a polyoxypropylene adduct of a polyoxyethylene glycolwherein the polyoxypropylene chain has a molecular weight of about 1000and the oxyethylene content is about 55 percent by weight of themixture.

The following examples are presented to illustrate the invention. Theresults were obtained with a laboratory digester. The laboratorydigester is known to correlate well with actual plant operations. Theprocedure employed was as follows:

This laboratory digester consists of a jacketed shell constructed of 316stainless steel with a tight fitting gasketed lid, secured by a lug boltand nut system. The system is pressure proof to 300 lbs./in. gage(Static Test) and the jacket is also proof to the same pressures. Thewood chip charge is contained in a stainless steel wire mesh basket(18-20 mesh). The digester is piped to allow circulation of cookingliquor at the start of and at intervals during a cook. Circulation ofthe liquor at cooking pressures is accomplished by a positivedisplacement pump of the rotary eccentric type. The circulation of thecooking liquor is from top to bottom of the digester.

The heating of the digester and charge is accomplished by the use oflive steam (maximum pressure available 140 lbs./in. gage). The steamsupply passes to a pressure regulator and then to the digester jacket(indirect heating) or directly to the digester charge in the shell(direct heating).

The digester is equipped with a condenser to condense the volatilemalodorous byproducts of cooking and a drainage system for removal ofthe black liquor at the end of the cook.

The digester was steamed to the maximum pressure required byincrementally increasing the pressure. At the end of 60 minutes thepressure reached -150 psig. The cooking cycle times ranged from 0.5 to3.0 hours. At the end of the cycle, the pressure was relieved rapidly byopening the gas-off valve and discharging the volatile malodorousby-products through a condenser. The black liquor was discharged to thesewer under slight pressure. The digester lid was removed whenatmospheric pressure was reached and the charge was washed with anamount of water five to six times the volume of the charge. The pulp wasdefibered at low consistency with a high-speed propeller agitator,screened through a 0.010 inch cut plate, collected and dewatered bycentrifuging using a 100 mesh wire screen belt. The yield was calculatedon an oven dry basis.

EXAMPLE 1 Wood: Loblolly Pine Chips Total Active Alkali, percent 16.5Sulphidity 26.0 Liquor-to-Wood Ratio 3/1 Maximum Pressure, psig.Temperature, F. 350 Additive, percent,

based on ovendried chips 0.2

Run Additive Yield 7c Increase in Yield 1 51.9 2 48.6 3 49.6 4 50.5 549.1 6 48.5 7 49.7 Ave. 49.7

8 Nonionic No. 3 58.6 9 Nonionic No. 3 55.7 10 Nonionic No. 3 562 Ave.Nonionic No. 3 56.8 14.3

11 Nonionic No. 2 53.7 12 Nonionic No. 2 54.1 13 Nonionic No. 2 52.0 14Nonionic No. 2 52.0 Ave. Nonionic No. 2 52.9 6.4

EXAMPLE l1 Wood: Loblolly Pine Chips Total Active Alkali. percent 21.25Sulphidity, percent 26 Liquor-to-Wood Ratio 3/1 Maximum Pressure, psig.130 Temperature, F. 350 Additive, percent,

based on oven-dried chips 0.2 Run Additive 72 Yield 7r Increase in Yield15 45.6 16 47.1 17 47. 1 l8 47.0 Ave. 46.5

l9 Nonionic No. 3 51.3 20 Nonionic No. 3 51.4

-Continued EXAMPLE 11 Wood: Loblolly Pine Chips Run Additive YieldIncrease in Yield Ave. 39.2

30 Nonionic No. 3 41.8 31 Nonionic No. 3 41.0 32 Nonionic No. 3 40.7 33Nonionic No. 3 42.4 Ave. Nonionic No. 3 41.5 5.9

34 Nonionic No. 1 42.9 35 Nonionic No. 1 43.6 36 Nonionic No. 1 41.7 37Nonionic N0. 1 42.2 Ave. Nonionic No. l 42.5 8.4

EXAMPLE IV Wood: Mixed Northern Hardwood Chips Total Active Alkali,percent 15 Sulphidity, percent 1 1 Liquor-to-Wood Ratio 5/ 1 MaximumPressure, psig. 96 Additive, percent,

based on oven-dried chips 0.2

Run Additive Yield 1 47.0 2 Nonionic No. 4 49.0 3 Nonionic No. l 54.2 4Nonionic No. 2 51.2

EXAMPLE V Wood: Mixed Southern Hardwood Chips Total Active Alkali,percent 21.5 Sulphidity, percent 26.0 Liquor-to-Wood Ratio 5/1 MaximumPressure, psig. 1 Additive, percent,

based on oven-dried chips 0.2

Run Additive Yield 1 43.4 2 Nonionic No. 1 46.7 3 Nonionic No.3 46.1

The effect of concentration of the nonionic surfactants is tabulated inExample V1, below. The cooking conditions employed were as follows:

EXAMPLE V1 Wood: Loblolly Pine Rescreened Chips Total Active Alkali,percent 21.5 Sulphidity, percent 26.0 Liquor-to-Wood Ratio 3/1 MaximumPressure, psig. 130 Maximum Temperature. F. 350

. /1 Increase Run Additive 7c 7: Yield in Yield Ave. v 45.0 7 NonionicNo. 1 I 0.2 49.2 8' Nonionic No. l 0.2 48.3 9 Nonionic'No. l 0.2 47.8 10Nonionic No. 1 0.2 47.8 Ave. Nonionic No. l 0.2 48.2 7.1

11 Nonionic No. 1 0.3 51.4 12 Nonionic No. 1 0.3 51.2 13 Nonionic No. 10.3 48.0- 14 Nonionic No. 1 0.3 49.6 Ave. Nonionic No. 1 0.3 50.0 11.1

15 Nonionic No. 1 0.4 46.4 16 Nonionic No. l 0.4 46.7 17 Nonionic No. 10.4 48.4 1.8 Nonionic No. 1 0.4 47.8 Ave. Nonionic No. 1 0.4 47.3 5.1

19 Nonionic No. 2 0.2 49.7 20 Nonionic N0. 2 0.2 48.8 Ave Nonionic No. 20.2 49.2 9.3

21 Nonionic No. 2 0.3 53.0 22 Nonionic No. 2 0.3 50.7 Ave. Nonionic No.2 0.3 51.8 15.1

23 Nonionic No. 2 0.4 52.5 24 Nonionic No. 2 0.4 52.9 Ave. Nonionic No.2 0.4 52.7 17.1

25 Nonionic No. 3 0.2 47.7 26 Nonionic No. 3 0.2 48.3 Ave. Nonionic No.3 0.2 48.0 6.7

27 Nonionic No. 3 0.3 50.9 28 Nonionic No. 3 0.3 49.6 Ave. Nonionic No.3 0.3 50.2 1 1.5

29 Nonionic N0. 3 0.4 50.0 30 Nonionic No. 3 0.4 48.0 Ave. Nonionic No.3 0.4 49.3 9.5

The burst and tear factors and the breaking length were determined at a500 Canadian Standard Freeness. These physical properties weredetermined according to the standard methods of the TechnicalAssociation of the Pulp and Paper Industry (TAPPI). The TAPPI standardsemployed were T404m, T403m and T4l4m. Table I below indicates that thechanges in these pulp properties as reflected by the percentage changein burst factor, tear factor and breaking length were essentiallyinsignificant. The sheets were prepared according to TAPPI standardsT205 and T220.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a process for the preparation of pulpwood by the digestion of woodchips in an aqueous alkaline liquor in which the total active alkaliconsists substantially of sodium sulfide and sodium hydroxide at amaximum temperature of 400 F., the improvement which comprises carryingout the digestion in the presence of a digester additive whose structurecorresponds to the formula zine, acetamide, succinamide,benzenesulfonamide, adipic acid, succinic acid, glutaric acid, aconiticacid, diglycollic acid, citric acid, glycollic acid and ethanolamine, mhas a value such that the oxypropylene chain has a molecular weight fromabout 900 to 25,000, and n has a value such that the weight ofoxyethylene groups constitutes from about 10 to Weight percent of themixture said digester additive is present in an amount of about 0.05 to1.0% based on the weight of oven dry wood to sufficiently increase thepulp yield.

2. The process according to claim 1 wherein the total active alkaliranges from about 15 to 22 percent of the oven-dried weight of woodchips.

3. The process according to claim 1 wherein the liquor-to-wood ratio isfrom about 3/1 to 5/1.

4. The process according to claim 1 wherein the concentration ofadditive ranges from about 0.1 to 0.5 percent of the oven dry weight ofwood chips.

5. The process according to claim 1 wherein the nucleus of the digesteradditive is ethylene glycol.

1. IN A PROCESS FOR THE PREPARATION OF PULPWOOD BY THE DIGESTION OF WOODCHIPS IN AN AQUEOUS ALKALINE LIQUOR IN WHICH THE TOTAL ACTIVE ALKALICONSISTS SUBSTANTILLY OF SODIUM SULFIDE AND SODIUM HYDROXIDE AT AMAXIMUM TEMPERATURE OF 400*F., THE IMPROVEMENT WHICH COMPRISES CARRYINGOUT THE DIGESTION IN THE PRESENCE OF A DIGESTER ADDITIVE WHOSE STRUCTURECORRESPONDS TO THE FORMULA
 2. The process according to claim 1 whereinthe total active alkali ranges from about 15 to 22 percent of theoven-dried weight of wood chips.
 3. The process according to claim 1wherein the liquor-to-wood ratio is from about 3/1 to 5/1.
 4. Theprocess according to claim 1 wherein the concentration of additiveranges from about 0.1 to 0.5 percent of the oven dry weight of woodchips.
 5. The process according to claim 1 wherein the nucleus of thedigester additive is ethylene glycol.